1. Field of the Invention
The present invention relates to a monitoring device for ladder program, and especially relates to a monitoring device for ladder program which is provided with a function of automatically extracting branch circuits led to a certain ladder circuit and collectively displaying the branch circuits.
2. Description of the Related Art
In creation of a ladder program, in verification (debug) of an operation of the ladder program, and in diagnosis of abnormality or the like in an operation, call of a relevant ladder circuit onto a screen from a ladder program is frequently performed. Therefore, a function of detecting and extracting a ladder circuit by using signals and instructions which are used in the target ladder circuit as conditions is often provided.
In general, in a case where a specific ladder circuit is searched from a ladder program, a signal used in the ladder circuit is designated and a ladder circuit in which the designated signal is included is detected so as to extract the target ladder circuit. A signal which is a detecting condition is generally designated by a letter string representing a name (an identifier), an address, and the like which are assigned to the signal. Further, an operator is notified of a result of detection such that a ladder circuit which is first determined to satisfy a condition is displayed on a screen or all ladder circuits which are determined to satisfy the condition are displayed in a list.
On the other hand, in a ladder program, an operation of the program can be branched by a jump instruction or a subroutine call instruction, and in a monitoring device for ladder program, a state of a signal which is a branching condition of a branch circuit representing such jump instruction, subroutine call instruction, and the like can be confirmed.
Further, as a prior art technique of extracting and displaying a ladder circuit, a monitoring device for ladder program which is provided with a function of extracting and displaying a plurality of ladder circuits which use a certain signal is disclosed (refer to Japanese Patent Application Laid-Open No. 5-134718, Japanese Patent Application Laid-Open No. 2003-084813, Japanese Patent Application Laid-Open No. 2008-204254, and Japanese Patent Application Laid-Open No. 2009-122936, for example).
In verification of an operation of a ladder program, when a certain ladder circuit does not operate, that is, when processing is skipped, it is necessary to confirm a branch circuit which represents a jump instruction, a subroutine call instruction, and the like and allows the ladder circuit which does not operate to perform.
In a case where this confirmation operation is performed by using the above-described prior art technique, a user is required to manually detect respective branch circuits which allow a ladder circuit which does not operate to perform in sequence to confirm a branching condition. However, manual detection and confirmation of branch circuits with respect to a large-size ladder program require a great deal of labor and impose a substantial burden on a user.